Anatomical Structure and Location of the Transversus Thoracis Under the Skin

Description

Seen through a semi-transparent anterior thoracic wall, the sternum lies in the midline with the costal cartilages of the upper ribs curving laterally to meet it, while the clavicles span superolaterally toward the acromial ends and the scapulae sit posterolaterally behind the rib cage. On the deep (internal) surface of the sternal body and xiphoid process, the transversus thoracis (sternocostalis) forms a thin, fan-like sheet whose slips run superolaterally to insert on the internal aspects of the costal cartilages, classically ribs 2 through 6. Intercostalis muscle layers occupy the intercostal spaces between adjacent ribs, with their fibers tracking obliquely across the thoracic cage. This is a deep, anterior compartment relationship, with transversus thoracis posterior to the sternum and medial to the intercostal musculature. Surgeons and proceduralists care about this plane because the internal thoracic artery and veins descend vertically just lateral to the sternum, immediately superficial to transversus thoracis before giving off anterior intercostal branches. A parasternal approach for pericardiocentesis, internal mammary vessel harvest for coronary artery bypass grafting, and median sternotomy closure all bring you into the neighborhood where transversus thoracis can be encountered or detached. Small muscle. Big landmark set. Use this illustration for thoracic wall teaching in gross anatomy and respiratory mechanics modules, for operative anatomy figures in cardiothoracic and breast reconstruction texts, and for patient-facing diagrams explaining why parasternal incisions and chest tube placements avoid the internal thoracic vascular bundle. Anatomical accuracy verified by SciePro's Medical Advisory Board.